§ l. Is Organism More than Mechanism? § 2. Chemical and Physical Laws apply to Organisms. § 3. Some Difficulties in the Application, of Physical and Chemical Formulæ to Organisms. § 4. Criticism of Mechanistic Descriptions of Everyday Functions. § 5. Criticism of Mechanistic Descriptions of Animal Behaviour. § 6. Difficulty of Applying Mechanistic Formulæ to Development. § 7. Difficulty of Applying Mechanistic Formulæ to Organic Evolution. § 8. Answers to Criticisms.
§ 1. Is Organism More than Mechanism?
ACCORDING to Kirchhoff's famous definition (1876), the task of mechanics is to describe completely and in the simplest manner the motions which take place in nature. When we give a mechanical description of an occurrencethe eruption of Vesuvius, the bursting of the broom-pods, or the curling of the non-living tendrils of a mermaid's purseit is in terms of matter and motion, or in chemico-physical terms which are believed to be reducible to those of matter and motion. The mechanical account is as such entirely satisfactory when it enables us to see a process as a continuous series of necessarily concatenated mechanical operations like those which occur in the slow movement of a glacier, or like the successive explosions which mark the extension of a rapidly spreading conflagration. We shall use the slightly wider term mechanistic to include either a matter-and-motion description, which is in the strict sense mechanical, or a more dynamical description in which the concept of energy is emphasised, or a chemico-physical description which is ideally mechanical,, that is, theoretically reducible to matter-and-motion description, though, as a matter of fact, the reduction may not have been as yet effected. A mechanistic description, in short, is in terms of the fundamental concepts of physics and chemistry; and it is the most precise and most thorough kind of description that is known.
Given three good observations of a comet, an astronomer who knows his business can prophesy with certainty when, barring accidents, it will return. He may not tell us what gravitation means, or what the comet is made of, or how it arose, or what it portends to mankind, but of the coming and going he gives a complete account, as the punctual return of the comet afterwards proves. Now the question which interests us at present is not whether the biologist, if he knew his business as well as the astronomer, could tell us at what precise date next spring the swallows will reach our shores, but rather whether the success of his prediction depends on the reduction of the swallows' behaviour to mechanistic formulation.
The question may be split into two. The first is: How far, as a matter of fact, can characteristically vital occurrences, such as the contraction of a muscle, be described in terms of the formulæ which serve for the study of tides and eclipses, the moulding of a dew-drop or the making of a star? One obvious limit is that, if the organism has mentality that counts in its agency, then the behaviour cannot be completely formulated in mechanical terms. Mind cannot be described in terms of matter, or emotion in terms of motion. As there are some biologists, such as Prof. Jacques Loeb, who hold a tropism theory of animal conduct which does not recognise mental factors as ver caus at all, and as there are organisms and vital activities which are not known to have any mental aspect, we shall leave this limit to mechanistic description for future consideration.
So the first question is whether, mentality apart, there are irreducible peculiarities in vital activitiespeculiarities which cannot be adequately accounted for in terms of physico-chemical or ideally mechanical description? Or is the usually admitted incompleteness of the physico-chemical description of, let us say, a reflex action merely temporary, and likely soon to disappear?
The second question is a little different. Of the movements of the heavenly bodies Gravitational Astronomy gives mechanical descriptions which are practically exhaustive and almost perfectly useful. Now, supposing there were available a complete mechanical account of, say, the opening of a Yucca flower, would that be all that is wanted in Biology? Would light have been thrown, for instance, on the fact that only one Yucca flower opens on each plant each evening, that the flowers begin to open when the Yucca moths begin to emerge from their cocoons, that the life of the flower and the life of the moth are closely bound up together, so that the one without the other is not made perfect? The Yucca flower and the Yucca moth are organisms with a history; they have come to work into one another's hands. Are their adaptive relations only different in degree from the dynamical relations between Earth and Moon, or must we admit that the answers to distinctively biological questions do not follow from even a complete ledger (were that available) of the chemical and physical transactions?
§ 2. Chemical and Physical Laws apply to Organisms.
The apartness of living creatures was stated by Kant in a famous passage. It is quite certain that we cannot become sufficiently acquainted with organised creatures and their hidden potentialities by aid of purely mechanical natural principles; much less can we explain them; and this is so certain, that we may boldly assert that it is absurd for man even to conceive such an idea, or to hope that a Newton may one day arise able to make the production of a blade of grass comprehensible, according to natural laws ordained by no intention; such an insight we must absolutely deny to man (Teleological Faculty of Judgment, § 74). We wonder how much of this he would have written had he known the bio-chemistry and bio-physics of to-day.
It is now recognised by allvitalists includedthat chemical and physical laws apply to living creaturesto what may be called their inorganic aspect. There is no confusion of categories in so doing. Chemically regarded, the living creature is of a piece with its surroundings; it contains no peculiar elements. The most essential substances, which are always present, are proteins, but there is nothing rare in their composition,just the carbon, hydrogen, oxygen, nitrogen, and so on of the surrounding world. The peculiarity of proteins is in the complexity of their molecules, which consist of a large number of atoms, and in their general occurrence in a colloid state, which has very important physical properties. It used to be thought that organic substances could be made only by the direct touch of life, but the synthetic chemist has built up samples of most of the different kinds with the exception of natural proteins. Even these are being approached, and their synthesis will probably be effected too.
Chemically regarded, living involves a complex of reactions in, or associated with the material which we call protoplasm and some of these reactions can be reproduced apart from the organism altogether. There are oxidations and reductions, hydrations and de-hydrations, fermentings and so on, which taken separately may be mimicked in the laboratory. By freezing tissues, grinding them in a mortar, and thawing and filtering the result, a non-living material can be obtained in which some chemical reactions go on. These can be studied in isolation, and this is one of the everyday methods of bio-chemistry. Similarly, chemical laws are of indispensable assistance in enabling us to understand bow the blood carries oxygen and carbon dioxide and how digestive juices change the food in the stomach.
In the same way it is certain that well-known physical processes occur in the living body. Capillarity plays some part when sap ascends in a tree, and evaporation plays some part when the leaves droop in the summer heat. Surface-tension is illustrated when an egg-cell becomes spherical, and the elasticity of connective tissue when a hen turns suddenly from scanning the sky to inspect a minute seed on the ground at her feet. We illustrate the action of levers when we walk, and the properties of lenses when an image is formed on our retina. All physiologists are agreed that, in the description of bodily functions, the formulæ of chemistry and physics carry us some way.
And just as the fundamental chemical fact, that no increase or decrease of matter ever occurs in a closed system, holds true for the living body and its environment, so it seems to be with the conservation of energy. An animal such as a dog, supposed for the sake of simplicity to be at rest, takes in potential energy in the form of food, and takes in oxygen to keep the vital combustion agoing. It uses up the energy in internal activities:the heart drives the blood round the body, the midriff rises and falls, the lungs empty and fill, and so on. Now, if we allow for the potential energy of waste-products and storage-products, we find that the heat given off is in accurate correspondence with the energy taken in. The accounts balance. The invention known as a calorimeter made it possible for Rubner to demonstrate that the heat-energy given off by an animal during a prolonged experiment was the equivalent of the food taken in, with a discrepancy of only 0.5 per cent., which is believed to be the all but inevitable discrepancy due to the conditions of experiment. There was a smaller discrepancy (0.1 per cent.) in Atwater's experiment of sixty-six days during which his students worked in a calorimeter. When they remained at rest, the discrepancy disappeared. It is plain, then, that the living of the animal is in general accordance with the big generalisationthat the sum total of energy in a closed system remains constant. One mode may change into another mode, but no energy ceases or is lost in the transformation.
It is certain that a chemical and physical description can be given of much that goes on in organisms, and this kind of description will certainly extend its scope. We need only refer to Professor Bayliss's Principles of Physiology as a fine illustration of the application of chemical and physical analysis to the activities of the living body, and to Professor D'Arcy Thompson's Growth and Form as its counterpart in the domain of morphology. At the same time it is important to notice that the working out of the chemico-physical description of vital activity is not altogether plain sailing. Let us illustrate.
§ 3. Some Difficulties in the Application of Physical and Chemical Formulæ to Organisms.
It is a general fact of experience that the rate of chemical reactions is accelerated by heat and retarded by cold. The illustrious chemist Van't Hoff formulated the law that the rate of a chemical process increases in geometric progression when the temperature is increased in algebraic progression. The velocity of the reaction may be doubled or trebled by a rise in temperature of 10° C. or reduced by one-half or more by a fall in temperature of 10° C. Now it has been observed that the rate of heart-beat of various animals, so widely separated as tortoise and water-flea, is reduced to about a half if the temperature be lowered 10° C., and the same holds of some other vital processes. Therefore it has been hastily concluded that the chemical processes associated with vital activities follow Van't Hoff's law in the way they vary in rate with changes in temperature. But it looks as if the conclusion had been premature. The increase in the rate of development of the eggs of the plaice is directly proportional to the increase in the temperature within the limits of viability (Dannevig, Johansen, Krogh); it does not illustrate Van't Hoff's law. In certain fishes, in frogs, water-beetles, and sea-urchins the Danish physiologist Krogh finds that the relation between the temperature and the rate of development cannot be expressed, even approximately, by Van't Hoff's formula. According to Krogh's experiments on frogs and goldfishes and some other animals, the influence of temperature on the standard metabolism, of which the absorption of oxygen is taken as an index, is regular and constant, and cannot be expressed either by Arrhenius's formula or by the rule of Van't Hoff. Ege and Krogh have shown that Van't Hoff's rule does not apply to the relation between temperature and the respiratory exchange in goldfishes. Indeed, there are many cases where Van't Hoff's rule does not seem to apply. It is said to hold good for such a subtle thing as the rate of cell-division in the growing point of a root, but this is not to be taken as indicating a simple chemical process. There appears to be a repertory of intricate processes, the peculiarities of which are mutually neutralised.
There are also some difficulties in regard to the transformations of energy in living creatures that make one hesitate to assert dogmatically that conclusions based on a study of the inorganic must hold true for organisms. It is possible, for instance, that living cells may act selectively in relation to the molecules that bombard them, and that the organism may be able in some measure to evade the second law of thermodynamics.
The best steam-engine is only able to change about 12 per cent. of its income of potential energy into work; the animal can change about 25 per cent., and is therefore from this point of view quite remarkably efficient. Moreover, as Professor Soddy points out, the organism has a capacity for dealing with kinds of chemical substances which cannot be converted by inanimate agencies into useful forms of energy without terrible waste. The chemical energy of food suffers direct transformation into work without first being converted into heat.
In any case it is well to remember that while there is a general, and for certain purposes very useful, applicability of chemical and physical laws to the activities of organisms, there are also in organisms novel circumstances which seem to alter cases.
In this connection, the Italian physicist and mathematician Enriques writes (1914, p. 376): Only a few general physical relations, persisting through all varieties of conditions, are found to be verified without change in the realm of biology, as, for example, the conservation of matter and of energy. But among the less extended laws that refer to diffusion or osmosis or electric conductivity, etc., we meet at every step with exceptions and apparent contradictions. He refers, for instance, to the fish known as the Torpedo, as a living Leyden jar, and says: While the functioning of an electrical machine is so easily hindered by the moisture of the insulator, here we see a charge which is not lost in the watery fluid with which the tissues of the animal are saturated. The living cells of the bladder hinder the diffusion, of water:We can only say that a moist tissue prevents the passage of water by virtue of being alive, for it loses this property as soon, as death has taken place. Enriques also refers to the work of Galeotti, who has shown that protoplasm hinders the diffusion of certain substances, and in certain cases offers an especial resistance to the ions moved by electro-motor force. It may be said that these difficulties are due to the particularly complex conditions. But in the meantime it is not unscientific to state that the analytical explanation is not as yet forthcoming. What is gained by advancing to a synthetic explanation, which starts with the fact of life, is another question to be considered later on.
So far, then, our conclusions are, (1) that many chemical and physical processes go on in the living body which are quite in line with those that occur in conditions apart from living creatures altogether; but (2) that at present, without going far, we are met by certain difficulties which suggest that we should be cautious before concluding that the physico-chemical re-descriptions of vital events are adequate or on the way towards adequacy. It is certain that some bodily occurrences admit of mechanistic description and that this is very useful, both practically and theoretically. Thus the production of animal heat, which was a riddle to the old physiologists, has in great measure been accounted for just as one might account for the heat in a, basin of water after electric discharges have been passed through. The clearing up of this problem may be practically useful to us on a cold day or to our physician if we are fevered. It has also been theoretically useful in the science of physiology, for instance because it brought into prominence the more intricate problem of the regulation of the body temperature, which does not seem to admit at present of mechanistic solution, This example seems to us to be typical. Along many lines we advance so far with mechanistic formulation, and then we are suddenly pulled up. Let us, then, methodically test the mechanistic descriptions of occurrences in the realm of organisms, keeping in view both the degree of completeness in the descriptions and their relevancy in biological study. It will conduce to clearness if we omit in the meantime all reference to conscious control. Let us consider (1) the everyday functions of the body, (2) animal behaviour, (3) development, and (4), very briefly, evolution.
§ 4. Criticism of Mechanistic Descriptions of Everyday Functions.
There has not yet been given any physico-chemical description of any total vital operation. Soon after the establishment of the doctrine of the conservation of energy, about the middle of the nineteenth century, there was a remarkable mechanistic boom. The impression became prevalent that the citadel of life was about to be taken by storm. Nerves were like wires along which electricity flowed; the kidney was a group of filters; respiration was a matter of the diffusion of gases; the passage of digested food from the alimentary canal to the blood-vessels was a process of osmosis; and so on.
The inevitable reaction followed; it was found that things were not so simple as they seemed. The physico-chemical descriptions leave out a good dealbig residual facts which seem to many to be the crucial facts. Dr. J. S. Haldane writes: The application to physiology of new physical and chemical methods and discoveries, and the work of generations of highly-trained investigators, have resulted in a vast increase of physiological knowledge, but have shown with ever-increasing clearness that physico-chemical explanations of elementary physiological processes are as remote as at any time in the past, and that they seem to physiologists of the present time far more remote than they appeared at the middle of last century (1913, p. 47).
In his contribution to Life and Finite Individuality (1918), Dr. J. S. Haldane says (p. 13): I need only refer to such activities as the oxidative processes in living tissues, the processes of secretion and absorption, or reflex action. There is a prevalent idea that the progress of chemistry, and particularly of physical chemistry, has furnished explanations of these processes. This is most certainly not the case. What physical chemistry has helped us to do is to obtain measures of the processes in the living body; but the results of measurements have been to show with ever-increasing clearness that the processes in the living body do not correspond with our conceptions of those in nonliving structures, and that we are not remotely in sight of mechanical explanations of the former.
As an example, I need only take the case of the exquisitely thin and delicate living membrance which separates the blood in the lung capillaries from the air in the alveoli or air-cells of the lungs. A short time ago it was assumed that this membrane plays only a passive part which we regard a non-living membrane as playing, and allows oxygen to diffuse through it just as a non-living membrane would. On applying accurate methods of measurement we found that, whenever there is need for an extra supply of oxygen, as, for instance, during muscular exertion, the membrane assumes an active rôle and pushes oxygen inwards, without regard to the mechanical laws of diffusion. In this respect the alveolar epithelium acts just like the epithelium of the swim-bladder, or that of the kidney or any other gland, or the alimentary canal. The progress of physical chemistry is enabling us to distinguish sharply between physiological activity and the processes occurring in non-living structures; and the establishment of the distinction is sweeping away the easy-going mechanistic explanations which became current during the latter half of last century. On the whole, there is no evidence of real progress towards a mechanistic explanation of life.
The inadequacy of the mechanical description is apparent when we consider any function in its totality. There is a correlated sequence of events, and it is the correlation that is characteristic. One group of cells has not only to do its own work, but has to keep in exact co-ordination with the working of other groups, sometimes at a distance. It goes without saying that we know a good deal about this internal regulationwe do not expect action without meansbut we cannot give a complete chemico-physical account of it. It is sometimes achieved by the nervous system, sometimes by the blood, sometimes by internal secretions. Dr. J. S. Haldane points out that a minute and scarcely measurable increase in the hydrogen ion concentration of the blood excites the respiratory centre of a normal warm-blooded animal to intense activity. Similar minute alterations in the concentration of water, or sugar, or sodium chloride, or hydrogen ions, have a corresponding influence on the secretory action of the kidney. It might be thought that a multiplication of items of facts of this sort would eventually give us precisely what we wanta coherent description of integration. But that is not in view as yet, for we have always to unite the chemico-physical facts by vital links, by postulating primary properties of the organism, referred to in Lecture III., which remain unreduced. Unless we do this we cannot explain how the numerous activities work in a variable way into one another's hands, how they are coordinated in a harmonious result, how they are adjusted in a regulatory fashion to the changeful environmental conditions.
The temperature of a furnace depends upon the amount of thorough combustion that can he made to take place within a given time, and on the arrangements to prevent waste, and so on. It can be kept from exceeding a certain limit, if the stoker cease to stoke or if the draught of air be lessened, or in other ways. Similarly, the temperature of the body in a warm-blooded animal is automatically regulated to a nicety so that, if it exceed the normal even by a very little, we know that something is seriously wrong. But there are great differences between the organism and the furnace. Thus in the organism the oxidation does not, like ordinary chemical oxidation, increase or diminish in proportion to the varying supply of oxygen brought to the seat of oxidation, but is controlled by living cells.
We can picture a complicated series of mechanical operations with here and there an intelligent workman who is essential because what is required is like very intricate shuntinga regulation, an adjustment, a co-ordination. So is it with the organism. We can give a chemico-physical account of isolated processes, but we cannot give a connected description of the whole without postulating the intervention of living cells. Not hypothetical agents, like Clerk-Maxwell's sorting demons, but observable living cells like Ambæ.
Let us take another illustration. When we strike a match we can give a complete chemico-physical account of the later phases of the process, apart, that is, from our own intention and movement. When we draw back our finger from a hot iron, are we illustrating more than a very complicated form of the match's response to the friction? According to Dr. J. S. Haldane, we are. In identifying stimulus and response with physical or chemical cause and effect, the mechanistic theory makes a gigantic leap in the dark.
When the sun's rays passing through a knot in a roof-light set fire to a heap of cotton-waste and the flames spread till they reach a barrel of gunpowder, which explodes, and other things happen, there is a chain of events which may be long or short, intricate or simple, but which is quite clearly stateable in chemico-physical, i.e., theoretically mechanical, language. But it is otherwise when a living structure responds to a stimulus. There is in reality no experimental evidence whatsoever that the process can be understood as one of physical and chemical causation. When we attempt to trace a connection we are lost in an indefinite maze of complex conditions, out of which the response emerges (Haldane, 1913, p. 34). A very familiar fact is that the same stimulus applied to two apparently similar animals or to the same animal at different times evokes different answers. We can indeed give reasons for this, but the reasons are not mechanical reasons.
Why is it that we cannot adequately describe the life of the organism in terms of chemistry and physics? Let us take an answer from the philosophical physiologist, already quoted, Dr. J. S. Haldane, in his contribution to Life and Finite Individuality (1918). Because the organism forms itself and keeps itself in working order and activity (p. 14), and the idea of a mechanism which is constantly maintaining or reproducing its own structure is self-contradictory (p. 16). Empirical observations with regard to the behaviour of living organisms point clearly to the conclusion that in each detail of organic structure, composition, environment, and activity there is a manifestation or expression of the life of the organism regarded as a whole which tends to persist. It is this manifestation which distinguishes biological phenomena; and, through all the temporary variations of structure, activity, composition, and environment, it can be traced more and more clearly with every year of advance in biological investigation. We can trace it through the ordinary metabolic phenomena in living organisms, as well as through the phenomena of senescence, death, and reproduction (p. 21).
The everyday life of any common animal is an extraordinarily complex affair. For what is a creature but a great and well-disciplined army with battalions which we call organs, and brigades which we call systems? It advances insurgently from day to day, always into new territory of time and spaceoften inhospitable or actively unfriendly; it holds itself together, it forages, it makes good its expenditure of explosives, it even recruits itself, it pitches a camp and strikes it again, it goes into entrenchments and winter-quarters, it retreats and lies low, it recovers itself, it has a forced march, it conquers (Thomson, Wonder of Life, 1914, p. 627). What the biologist wishes is not merely a complete ledger of all the osmotic and capillary processes in the body, all the oxidations and reductions, all the solutions and fermentations,though that will be a great achievementhe wishes a description of the organism's daily march which will not ignore the correlated organismal tactics or the strategy which, in some cases at least, lies behind these.
§ 5. Criticism of Mechanistic Descriptions of Animal Behaviour.
Let us pass from the everyday functions of the body to a connected series of external activitiesto animal behaviour, a subject to which we shall return in the sixth lecture. We know that a young British-born swallow which leaves us for the south towards the end of summer may return the following spring to the parish, even to the farm-steading, of its birth,moved, who shall say by what deep compelling constitutional homesickness. Professor Yung of Geneva took twenty bees from a hive near the lake, put them into a box, and carried them six kilometres into the country, where he set them free. Seventeen returned to the hive, some of them in an hour.
The fresh-water mussel carries her young ones in her outer gill plate, and keeps them there, even long after they are ready to emerge, until a stickleback or a minnow comes into the immediate vicinity. When the fish comes near, the mother-mussel, whom it is no libel to call acephalous, liberates a crowd of the pinhead-like larvæ, which swim out into the water, snapping their tiny toothed valves, and secreting viscid attaching threads. They have the beginnings of a nervous system; they are sensitised to some stimulus from the fish; they fasten on to it and begin another chapter of their life. Even in the laboratory, when they have been removed from the mother, they become extraordinarily excited if a morsel of minnow be dropped into the dish in which they are. They respond definitely to the only stimulus which will enable them to continue their life. In some North American fresh-water mussels only one particular kind of fish will serve the purpose of temporary host.
In the remarkable life-history of the liver-fluke of the sheep, microscopic ciliated larvæ emerge from egg-cases which have fallen into water. These larvæ have no organs in the strict sense, no hint of a nervous system, and only a few cells altogether. They have energy enough to go on swimming for about a day in the water-pool. They may come in contact with many things, sticks and straws, roots of aquatic plants and various aquatic animals, but there is (in Britain) only one touch to which they respondthat of the small fresh-water snail, Limnæa truncatula, the only host that will enable them to continue their life-history. When they touch the mollusc they work their way into it and exhibit a remarkable succession of multiplications and metamorphoses. The point is that a minute, brainless creature responds at once to the one stimulus which will enable it to continue its life.
These instances have been taken from different levels: the swallow is very intelligent and yet instinctive, the bee is very instinctive and yet intelligent, the larval mussel has just the beginnings of a nervous system, the larval fluke has none. Our point is that we can find objectively analogous kinds of behaviour at all levels of nervous organisation, and that we have to do with a general capacity of living creaturesthe capacity of enregistering past experiences and experiments, either individual or racial, so that present behaviour is influenced by them in very specific ways. There are several characteristic features in behaviour which appear to be beyond all mechanical description. The behaviour is made up of a succession of acts which are correlated in a particular sequence. At any one moment there are chemical and physical processes going on, about which we know or may know a good deal, but it is the bond of union that eludes the chemist and physicist. To take items in the process and reduce them (as far as we can) to physical and chemical common denominators is interesting in its way, and for certain purposes useful, but it does not make any clearer the interlinking, the co-ordination, of all the items in a piece of behaviour. When we consider the larval liver-fluke arrested by contact with the fresh-water snailwith a particular species of water-snail, or the larval mussel arrested by the proximity of a minnow, or a stickleback, or, it may be, by one and only one particular species of fish, we are face to face with a common and characteristic feature in animal behaviour, that the creature is historically tuned to be a receptor of a unique but absolutely indispensable stimulus which may not occur more than once in the life-history. We may find perhaps some analogies to this in the inorganic worldfrom our point of view it would be strange if there were notbut it is supra-mechanical. By which we mean that it requires other than mechanical concepts for its formulationespecially the concept of the organism as a historic being.
Sometimes, it must be confessed, even the postulate of historic enregistering does not help us very much as yet, witness the well-known riddle of the homing of birds. Prof. J. B. Watson and Dr. K. S. Lashley took four nesting terns (two noddies and two sooties) from Bird Key in the Tortugas to Havana, 108 miles off, and liberated them in the harbour there. They were back at Bird Key next day, having probably spent most of the time recuperating around the shores of Cuba. Of five birds liberated off Cape Hatteras, in waters which these terns never visit, for Bird Key is the northern limit of their migratory range, at least three returned to their nests in a few days, having accomplished a journey of 850 miles as the crow flies, and of much more if the alongshore route was followed. Four noddies and four sooties were taken in a hooded cage on a Galveston steamer and liberated at a point in the middle of the Gulf of Mexico, 461 statute miles from home, and out of sight of everything. On release, all birds, with one exception, started eastwards. That one headed westwards and continued for about 200 yards, then turned suddenly towards the east. The birds had a strong head wind against them throughout the first day, but two of them returned to their nests in safety across the waste of seas. This seems to us so different from the return of the boomerang to the thrower's hand that we venture to call it different in kind.
When we are dealing with higher animals, presumably with conscious processes analogous to our own, the contrast with a mechanism stands out even more clearly. An engine overcomes hindrances, force against force, but it has no resource, no alternatives, no tactics. But an organism with a mind at work, a conscious organism, is different in its relation to hindrances. As Dr. J. S. Haldane says, It is aware of, and avoids, neutralises, or even takes advantage of them. It adapts its behaviour in such a manner as to maintain itself in the presence of what is outside the mere organic unity of its life. But in so doing the organism shows itself to be more than a mere organism; it includes within the unity of its life what seemed to be independent (Life and Finite Individuality, p. 23).
§ 6. Difficulty of Applying Mechanistic Formul to Development.
Our third test of mechanistic interpretation is with regard to development. When we watch a transparent marine animal, such as one of the Salps, we can see the movements of internal partsthe beating of the heart, for instanceand though what we see is not like anything in inorganic nature, we are reminded of a smoothly-working machine like a chronometer. On the other hand, when we have the good fortune to observe a development actually going on in perfect translucency, for instance in the egg of the moth Botys hyalinalis, our unprejudiced impression must surely be, that this is very far away from anything mechanical, that it is in fact very unlike anything else in the world. When we take the most familiar case of all, the development of the chick in the course of twenty-one days from a minute drop of living matter lying on the top of the yolkthe gradual emergence of the obviously complex from the apparently simplewe feel how true it is still, what Harvey wrote three centuries ago:Neither the schools of physicians nor Aristotle's discerning brain have disclosed the manner how the cock and its seed doth mint and coin the chicken out of the egg. It is not surprising that the facts of generation and development have often led naturalists to the conclusion that the categories of mechanism fall short in the domain of the organic. What particular facts of development seem to require more than mechanical description? There is the condensation of the inheritance into the microscopically minute germ-cellan extraordinary telescoping of individuality, of which we can form no image. It is quite true that there is within egg-cells a demonstrable complexity of organisation far greater than used to be supposed, that the nucleus is a little world in itself, that there is a growing knowledge of extremely minute, yet often distinctive, organ-forming plastosomes in the cytoplasm of the egg, that the artificial removal of part of the egg-cell is sometimes, as in Ascidians, followed by the non-development of a particular structure in the embryo, and so on. More and more we are coming to see in the germ-cell an implicit individuality with complex and specific organisation. But no sooner have we got this idea clearly focused in the mind than we are confronted with such facts as those of merogony, that a fragment of an egg-cell is able to develop into a normal embryo. It may be an argumentum ad ignorantiam, but if it be held, as the mechanists hold, that the egg-cell is completely describable as a chemico-physical mechanism of great complexity, it is not unfair to recall some of the difficulties,that the supposed mechanism has to form in fertilisation a working unity with another mechanism as complex as itself; that it has thereafter to divide over and over again; that a part is sometimes as good as a whole; and so on. It is sometimes easy to get twins from one egg by shaking the first two cleavage-cells apart, and even at the four-cell stage of the lancelet's development the same method may result in quadruplets. It almost seems as if we here reached a Euclidean reductio ad absurdum of a mechanistic interpretation.
The central problem of development is differentiation, and the biological study of this is not more than incipient. We cannot even elucidate the fact that the two cells into which a germ-cell divides are sometimes exactly alike and sometimes distinctly different. Out of apparent simplicity there gradually emerges obvious complexity. As Roux puts it, there is a self-manifestation of intrinsic manifoldness. What was a clear drop a few hours ago is now a manifest organism with nerve and sense-organ, food-canal and muscle. It is the most wonderful thing in the world. Sometimes the whole scene has changed when we return to observation after the interruption of an hour's lecture. Be it understood that no theory explains it, but while the biological interpretation may try with some success to bring development into line with, say, the organism's characteristic self-repairing activity, the mechanistic interpretation has not yet begun its task. It is a mere impious opinion that development will one day be described in terms of mechanics.
Another prominent fact in development is its regulatedness or correlation. Driesch and others have directed attention to the power the embryo often shows of righting itself after the building materials of its edifice have been artificially disarranged, of re-adjusting itself after the proportions have been artificially disturbed. A fertilised egg-cell frequently divides into a ball of cells like a microscopic mulberry fruit; the constituents of this ball may be disarranged and the ball pressed out of shape between two glass plates; yet if the interference be not too prolonged, the developing embryo may right itself and develop normally. Can we think of a machine which is practically unaffected if we cut off half of it, or which, being scrapped, patiently re-arranges its parts and begins over again!
If the developing organism is in its behaviour conationalthat is to say, on the way to being purposefulthe difference between it and a developing sidereal system is great. But what grain of evidence is there of this conational element? Not perhaps very much when we confine our attention to normal embryonic stages, where one phase appears to be the natural and necessary outcome of its antecedent. But we get another impression when we consider some of Driesch's cases of self-regulation and of re-adjustment after profound dislocation.
Whatever we make of it, one of the marvels of development is the manner in which separate parts are often correlated, as it were conspiring together towards some future result. In the making of the Vertebrate eye, an outgrowth from the brain forms the retinal cup, an independent in-growth from the skin forms the lens, some mesoderm cells migrate into the interior to form the vitreous humour, others combine to form the protective envelopes, and so on. Strange anticipations of coming events are well known to embryologists.
In a trivial detail, such as the making of the silk-like threads composing the skeleton of the common bath sponge, large numbers of secretory cells called spongoblasts group themselves in double file every here and there throughout the middle stratum of the sponge, as if some unseen captain marshalled them. Up the middle of the double file the spongin is secreted, made at the expense of the living matter of the spongoblasts, and the many individual contributions coalesce into a spongin-fibre.
In his Science and Philosophy of the Organism (1908), Driesch has with unexampled thoroughness and subtlety tested the possibilities of mechanistic description with particular reference to the facts of development. He reaches a conclusion of the first importance:No kind of causality based upon the constellations of single physical and chemical acts can account for organic individual development; this development is not to be explained by any hypothesis about configuration of physical and chemical agents. Life, at least morphogenesis, is not a specialised arrangement of inorganic events; biology, therefore, is not applied physics and chemistry; life is something apart, and biology is an independent science. But what, it may be said, of the science of developmental mechanics and of the lengthening row of volumes entitled Archiv für Entwick-lungsmechanik? The first answer is, that, after all, the developing embryo is a material system, and must exhibit chemical and physical means. Development shows a continuous action and reaction between an implicit organisation and the environing conditions, and developmental mechanics so-called is in great part concerned with discovering the correlation between steps in development and their appropriate external stimulation and nurture. These correlations are of great interest, but as our knowledge of them increases we do not get appreciably nearer a mechanical description of development. We do, however, recognise more and more that physical and chemical processes are in evidence.
The second answer is that the word mechanical is sometimes applied illegitimately to a systematic or connected account which displays a series of events in causal coherence without the intervention of mentality. Given certain properties of organisms in general, of nerve-cells and muscle-fibres in particular, we may give a more or less connected and complete account of a reflex action without dragging in any psychical agency. But this should not be called a mechanical description. It is simply, what it pretends to be, a physiological or biological description, and it implies various non-mechanical concepts. Similarly, given the organism's power of registration and of persistently reproducing its specific organisation, given the cell's mysterious power of dividingof dividing now into similar, and again into dissimilar halves, given the capacity of utilising nurtural stimuli to educe the inherent manifoldness of the germ, and so forth, we can make a show of discovering the connectedness, and inevitableness of the successive stages in development. But we cannot without abuse of terms speak of this as a mechanical description.
§ 7. Difficulty of Applying Mechanistic Formulæ to Organic Evolution.
As a fourth test of the adequacy of mechanistic description in the realm of organisms, we may refer very briefly to evolution, which will engage our attention in detail by and by. Such phrases as cosmic evolution and inorganic evolution are apt to suggest the mistaken idea that organic evolution is simply a continuation of a historical inorganic process of increasing differentiation and heterogeneity. It may be continuous with it, but it is not a continuation of it, any more than the evolution of human societary forms is a continuation of the evolution of mammals. The issues changed when organisms began, and again when man began.
Moreover, what is called, for instance, the evolution of the solar system should rather be called the development of the solar system, since it is the differentiation of one mass into explicit manifoldness. The originative nebula or whirling mass of planetesimals is comparable to a great world-egg, to borrow Hume's phrase, and we may think of it as developing into several embryos, as eggs sometimes do. But, so far as we know, there was no struggle between the various planets, or between them and their environmental limitations. There was no sifting process which eliminated some and left others surviving. Whether we speak of the history, or differentiation, or development, or evolution of the solar system, we must recognise that it was a very different process from organic evolution. In the former there were no alternatives, no trial-and-error methods. There was nothing comparable to the staking of individual lives and losing them which is characteristic of that sublime adventure which we call organic evolution. The theory of organic evolution starts with the assumption of variability, which transcends mechanical interpretation and is perhaps least obscure at present when we think of it most anthropomorphically as experimenting in self-expression. Moreover, the organism is in some measure a genuine agent even in the process of natural selection. It is often anything but a passive pawn. It does not simply submit to the apparently inevitable. It often evades its fate by a change of habit or of environment; it compromises, it experiments, it is full of device and endeavour. The evolving organism is a historical psycho-physical being, an agency trading with time; and the humblest creatures are in their mutations creative. Such mechanical description as is possible leaves the essential features undescribed.
The result of our consideration is that while mechanical description has its place and utility in the organic domain, it is inadequate to cover the characteristic facts of everyday functioning, of animal behaviour, of individual development, and of racial evolution. For all these demand other than mechanical concepts.
Our study has led us away from the view that there is only one science of nature, consisting of precise chemico-physical descriptions which have been, or are in process of being, summed up in mechanical or mathematical terms. As it seems to us, there is greater utility and accuracy in frankly recognising successive orders of facts, each with its dominant categories. There is the domain of the inorganic, the physico-chemical order, where mechanism perhaps has it all its own way. There is the realm of organisms, the biological order, where mechanism is checkmated by organism. There is the kingdom of man, the social order, where mechanism is transcended and personality reigns. Another grouping would be inorganic, animate, and psychical, but we wish to emphasise the apartness of man which has been obscured by the Darwinian theorytrue as that is.
These orders, which we separate that we may conquer them scientifically, do as a matter of fact overlap. The inorganic overlaps the organic, for organisms are material systems, and their living implies a concatenation of chemico-physical processes. But organisms require a science for themselves. The organic overlaps the human, for Man is affiliated to mammals, and his personality is tethered to protoplasm. But Man requires a science for himself. Or, if one prefers it, the organic overlaps the psychical, since the mind has a body, so to speak, and the spirit works in part through the flesh. And, looking in the other direction, who can be quite sure that the domain of the inorganic is as thoroughly exhausted by mechanical formulation as is usually supposed?
The important point is that the sciences are differentiated not merely by their subject-matter, but by their characteristic questions and methods and concepts. In this sense we claim autonomy for biology.
In so doing we are not in the least weakening the hope and endeavour that biology may approximate more closely to the position of an exact science. Our sole proviso is that this is not to be attained by the naïve device of leaving life out. The honourable rank of exactness is not to be allowed to remain the prerogative of sciences which deal with processes that can be described by aid of elementary corpuscles having ideal motions. It may be attained by all sciences that have resolutely begun to measure, including in measurement every form of precise registration. Thus not a little of modern psychology is very exact; although a description of its subject-matter in terms of ideal motions is certainly not its end! Biology is inexact compared with gravitational astronomy, partly because there have been more first-class minds among the astronomers than among the biologists, partly because in biology we deal with phenomena which are more difficult to measure than those with which astronomy deals, but mainly because biology has to deal with individualities which are variable and spontaneous, always to some extent unpredictable. It must be granted, however, that there has been a strong modern movement towards exactness even in the most difficult departments of biology. There has been for a long time much exact science in comparative anatomy and comparative physiology, but the recent labours of the biometricians on the one hand, and of the experimenters in genetics on the other, have already done much to bring the study of evolution problems nearer the ideal of exact science. In fact, as has been sagaciously pointed out, biology has already become a science to a degree that Kant deemed impossible, and this achievement helps to keep the biologist from admitting the validity of Kant's view that there is only one science of Nature.
§ 8. Answers to Criticisms.
Our argument may perhaps be strengthened by meeting some criticisms brought against what may be called the biological position.
(a) It has been suggested that those who think that vital phenomena require special biological categories are underrating what physico-chemical material systems can do. Many a machine is constructed to oil itself the more copiously when it works the faster, and the printing-press, as we urge it to put out more newspapers on the one side, pulls in more blank paper on the other(D'Arcy W. Thompson, Life and Finite Individuality, p. 37). Now there is undoubted utility in comparing a living creature with a machine, especially a machine with automatic regulatory arrangements. Both are systems effecting the transformation of matter and energy; both illustrate the co-operation of many parts to an effective result. But the living creature is always working, even in dying, towards its own preservation; it can adjust its activity to varying needs and circumstances; it can rest and begin again; in normal conditions it can give rise to another organism with activities like its own. The explicit organism develops in appropriate conditions from the implicit organism or germ-cell; if disturbed it can re-arrange itself; if it loses a part it can replace it; if it is broken into fragments it can sometimes reconstruct its living edifice.
(b) Those who claim autonomy for biology are sometimes rebuked by a reference to the music of the spheres. We are told that in Nature herself, if we look at her larger handiwork, self-regulation and self-maintenance become paramount attributes and characteristics of her machines. The solar system, qua mechanism, is the perfect specimen, the very type and norm, of a self-maintaining, self-regulating mechanism; and so also, grade after grade, are its dependent mechanisms, such as the world-wide currents of the atmosphere and of the sea (D'Arcy W. Thompson, Life and Finite Individuality, p. 37).
The order and balance of Nature's larger handiwork must indeed be recognised and admired. The same laws that are used in formulating cosmic architecture and regularity may be usefully employed, as we have admitted, in the realms of organisms. But our point is that the animalcule is in a way greater than all the stars, as stars, for it is an agent, it has alternatives, it shows experimental indeterminism, it commands its course. And when this began it was something new in the world.
(c) But where, precisely, it is asked, does the mechanistic description fail? The answer is twofold, that as yet it fails all along the line in thoroughness of description, and that it does not give us the kind of answer that as biologists we want. No student of science could have anything but delight in learning that the contraction of a muscle, or a reflex action, or the movements of an Amba had been satisfactorily described in terms of chemistry and physics. But it has not been done as yet in the case of any single vital activity. Diffusion plays its part in the interchange of gases in the lungs, but the lining epithelium of the air-sacs behaves, Dr. J. S. Haldane tells us, in a way which modifies diffusion processes, and that elusive modification keeps us alive. In the second place, the mechanistic description, even if it attained to the completeness of a ledger of all the chemical and physical processes in a piece of behaviour, would not thereby give us a natural history description of the behaviour. We need historical or genetic concepts. So we do not propose to sum up the ways of a starfish as those of a physico-chemical machine.
(d) The distinctively biological position admits that physical and chemical formulæ, concepts, or categories are applicable to organisms, but argues that they are inadequate, notably, for instance, because life is always in a sense history. But has not the line of physiological progress been mechanistic? The answer is that it is part of the method of science to abstract, and that it has been of great service to corner off and analyse physical and chemical operations which occur in organisms. But the success that has attended the study of the chemistry of the blood or the study of the optics of the eye, does not prove that the physico-chemical description of a living creature is or can be adequate.
(e) A thoroughly sound criticism is, that the concepts of physics and chemistry are not stationary but in process of development, so that any argument we use to-day about the irreducibility of vital phenomena refers only to modern chemistry and physics (unluckily, to be frank, to what we happen to understand of that chemistry and physics). The only answer to this criticism is that at any given time we must use the science we have got. No judgment in regard to irreducibility can be prophetic, unless we feel confident that we are dealing with generic differences, such as those between a conscious organism and a crystal.
(f) Finally, some would ask whether it matters much after all whether a chemico-physical formulation of a living organism is possible or not. Is there any depreciation of the lily-muffled hum of a summer bee if it be coupled with the spinning stars? The answer is twofold:(1) that science is all for veracity, and that the matter-and-motion summing up of an organism seems to many to be at present a false simplicity; and (2) that the treatment of a living creature, say horse or dog, as exhaustible in chemical and physical terms does not seem the way to get the most or best out of them. A physician's success in treating his patient from the purely chemical aspect is often remarkable, but it may be eventually necessary to recognise other aspects!
We agree, however, that what really matters is, that our view of the living creature be thoroughly well-informed. Whether our theoretical interpretation of it be, that it is like a very subtle engine or an intricate solar system, or that it is a system in which a new aspect of reality has manifested itself so that special biological categories are required, the most important thing is that we appreciate the facts of the case. When the methods of theoretical discussion have been exhausted, and it is doubtful whether they have ever made any biologist change his mind from a position to which personal experience had led him, the practical conclusion is that we must keep as close as we can to the observable realities, for it is in touch with these that we are most likely to get fresh light.
Chemically considered, the organism is of a piece with its surroundings (though very much more complex than any mere thing); it may be usefully studied by chemical methods; it exhibits many chemical processes which can be studied in isolation. Similarly, many well-known physical processes occur in the living body, and there is in its activity no known contradiction of the law of the conservation of energy. A chemical and physical (i.e., theoretically mechanical) description can be given of much that goes on in the living body, and this kind of description will certainly extend its scope. At the same time, there are difficulties in this chemico-physical description; some vital processes do not illustrate Van't Hoff's rule and it sometimes seems as if the organism were able to effect some evasion of the second law of thermodynamics.
But while chemical and physical (ideally mechanical) description has its place and usefulness in the organic realm, it is inadequate to answer the distinctively biological questions. It does not cover the characteristic facts of life.
If we consider the everyday functions of the body, we find that there has not been given any chemico-physical description of any total vital operation, such as the contraction of a muscle. We cannot satisfactorily describe in mechanical terms either the concatenation of events in a function or the correlation of one set of events with another set. This is still more marked when we consider animal behaviour, with its co-ordination of acts in an effective series.
As to individual development, we cannot give a mechanical description of the condensation of the inheritance into a germ-cell, or of the differentiation of the embryo, or of the regulation-phenomena observed when an embryo rights itself after the building materials of its living edifice have been seriously disarranged, or of the way in which many developing parts seem to conspire towards one result. Similarly, as regards organic evolution, we cannot offer a mechanical theory of variability, and the process of selection is more than mechanical sifting. The evolving organism is a historical psycho-physical being, an agency trading with time; and the humblest creatures are in their mutations creative.
The conclusion is thus arrived at, that mechanical formulæ do not suffice for answering biological questions.